This invention relates generally to heating devices for water heaters; and more particularly to a heat pump used to heat the water in a water heater.
Heat pumps have been used before to heat water for water heater installations. Examples of these uses are illustrated by U.S. Pat. Nos. 2,125,842 and 4,091,994. U.S. Pat. No. 2,125,842 discloses the submersion of the heat pump condenser coil directly in the water in the heater water tank as well as positioning of the condenser heat exchanger externally of the heater water tank and circulating the water through the condenser by withdrawing it from the lower end of the tank and returning it to the upper end of the tank. U.S. Pat. No. 4,091,994 discloses positioning the condenser coil around the outside of the heater water receptacle so that the condenser transfers heat to water in the tank through the tank wall itself.
These prior art water heater heat pumps have not found widespread use even though they are markedly more energy-efficient than typical electrical resistance heated water heaters. This is due to the fact that hot water recovery rate of such devices is generally unacceptably low and that these devices generally required the purchase of both the water tank and the heat pump mechanism thereby not affording the user the opportunity to keep an existing water heater.